The invention relates to an instrument for subjecting a liquid-absorbent article to controlled pressure during experimental liquid-absorbency procedures. Pressure is exerted on the sample by the intermediary of a flexible membrane to achieve a more uniform pressure distribution. The invention also extends to a method for conditioning a liquid-absorbent article by the application of pressure for conducting liquid-absorbency tests.
Manufacturers of disposable absorbent articles such as sanitary napkins, diapers, adult briefs, urinary pads, wound dressings, nursing pads, tampons, or desiccants to keep goods dry during shipping and storage typically perform numerous absorbency tests on proposed new designs to attain full comprehension of their behaviour. It is often useful to test the absorbent properties of such articles under pressure. Generally, this is accomplished by placing the absorbent article to be tested between two rigid plates that are vertically movable one with relation to the other. Dead weights are then placed on the upper plate to obtain the desired pressure level. An access port in the upper plate allows the laboratory technician to feed test liquid to the sample or to insert in the pressure cell the probe of a measurement device.
The procedure described above is suitable if the sample has a planar configuration and remains dimensionally stable when wetted. This pressure cell, however, is inapt for handling anatomically shaped absorbent products because the pressure distribution created by the rigid plates is far from being uniform. The same problem is observed with most fluff-based products that collapse when placed in contact with liquid. It will become apparent that once the test liquid is delivered to the sample, the region surrounding the point of impact abruptly shrinks which causes a pressure depletion in that area. The reverse problem is observed with materials containing sphagnum moss or superabsorbents that swell up upon absorption of liquid. In those cases, the injection of liquid in the sample causes a pressure concentration in the wetted zone.
Pressure discrepancies along the sample should be reduced as much as possible, otherwise the test results may be corrupted. Accordingly, it is desirable to provide a pressure cell capable of subjecting absorbent samples that are non-planar or undergo dimensional changes upon wetting to more uniform pressures during liquid-absorbency tests.
An object of the invention is a pressure cell for conducting liquid-absorbency experimental procedures, which is capable of subjecting the sample to a more uniform pressure than prior art devices.
Another object of the invention is an improved method for conditioning a liquid-absorbent article by the application of pressure during experimental liquid-absorbency procedures.
As embodied and broadly described herein, the invention provides a pressure cell for conditioning a liquid-absorbent article by the application of compressive stress thereon during a liquid-absorbency test (For the purpose of this specification, xe2x80x9cliquid-absorbency testxe2x80x9d shall mean an experimental procedure for ascertaining a quality of the absorbent article that has connection, relation or reference to absorption of liquid. The experimental procedure may or may not involve a transfer of liquid to the sample under observation.), said pressure cell comprising:
an abutment member;
a variable volume chamber including a flexible membrane, said abutment member and said flexible membrane defining therebetween a three-dimensional space for receiving the liquid-absorbent article, said variable volume chamber being inflatable by injection of pressurized fluid therein to cause said flexible membrane to compress the liquid-absorbent article while conforming thereto, whereby said pressure cell allows to conduct a liquid-absorbency test on the liquid-absorbent article in a compressed condition between said flexible membrane and said abutment member.
In a preferred embodiment, the pressure cell comprises a frame made of two rigid plates vertically spaced from one another. A bag of supple plastic material, polyethylene for example, is laid on the bottom plate. The absorbent article to be tested is placed between the flexible bag and the upper plate, and the bag is inflated by injection of compressed air. In the inflated condition, the bag compresses the absorbent article against the upper plate while conforming to its tri-dimensional configuration to achieve a uniform pressure distribution. It will also be apparent that the flexible bag manifests a dynamic adaptive behaviour when the sample undergoes dimensional changes upon absorption of liquid. For instance, if the sample locally swells-up or shrinks, the bag follows the shape evolution to maintain the pressure loading substantially uniform.
As embodied and broadly described herein, the invention also provides a method for conditioning a liquid-absorbent article by the application of pressure to the liquid-absorbent article during a liquid-absorbency test, said method comprising the steps of:
placing the liquid-absorbent article between an abutment member and a flexible membrane forming a wall of an inflatable bag;
injecting pressurized fluid in said bag to cause said flexible membrane to compress the liquid-absorbent article while conforming thereto, whereby allowing to conduct a liquid-absorbency test on the liquid-absorbent article while maintaining the liquid-absorbent article in a compressed condition between said flexible membrane and said abutment member.